1. Field of the Invention
The present invention relates to a light guiding body used for illumination, an illuminating device including the light guiding body, an image reading apparatus including the illuminating device, and an image forming apparatus.
2. Description of the Related Art
As this kind of illuminating device, for example, a device disclosed in JP 2000-089030 A (hereinafter referred to as “Patent Document 1”) is known. In Patent Document 1, a light emitting surface is formed on a side surface of a columnar-shaped light guiding body along the longitudinal direction thereof. Also, a sawtooth-shaped light reflecting surface is formed on the other side surface of the light guiding body along the longitudinal direction thereof, thus, the light emitting surface and the light reflecting surface are opposite to each other. Then, light from a light emitting device (light source) is incident to an end surface of the light guiding body in the longitudinal direction so that the light is propagated in the light guiding body. The light is directly emitted from the light emitting surface of the light guiding body, and furthermore is reflected by the light reflecting surface so as to be emitted from the light emitting surface. Thus, a surface of an original is illuminated by the emitted light. Also, an inclination angle distribution of the respective inclined surfaces that form the sawtooth-shaped light reflecting surface is adjusted so that an emitted light quantity distribution emitted from the light emitting surface is suitably set.
Also, in JP 2011-188080 A (hereinafter referred to as Patent Document 2), a light emitting surface having a cross sectional shape of a semicircle is formed on a side surface of a columnar-shaped light guiding body along the longitudinal direction thereof. A light scattering surface is formed on the other side surface of the light guiding body along the longitudinal direction thereof, thus, the light emitting surface and the light scattering surface are opposite to each other. Also, a plurality of light emitting devices is disposed on an end surface of the light guiding body. Then, light from each light emitting device is incident to the end surface of the light guiding body so that the light is propagated in the light guiding body. The light is directly emitted from the light emitting surface, and furthermore is reflected by the light scattering surface so as to be emitted from the light emitting surface. Thus, a surface of an original is illuminated by the emitted light. Also, positions of the respective light emitting devices are adjusted so that the emitted light quantity distribution emitted from the light emitting surface is suitably set.
In this kind of image reading apparatus, the original is illuminated by an illuminating device below a glass while transported on the glass in the sub-scanning direction, thus an image sensor such as a CCD (Charge Coupled Device) reads the original by repeatedly scanning the original in the main-scanning direction. Or, the original is positioned and placed on the glass, and while the illuminating device and the image sensor are moved in the sub-scanning direction below the glass, the illuminating device illuminates the original so that the image sensor reads the original by repeatedly scanning the original in the main-scanning direction. Various illuminating devices that illuminate the original are known, for example, a fluorescent lamp and an LED array are used.
In JP 2010-119054 A (hereinafter referred to as Patent Document 3), JP 2012-160866 A (hereinafter referred to as Patent Document 4) and JP 2012-212069 A (hereinafter referred to as Patent Document 5), LEDs are disposed at both ends of a columnar-shaped light guiding body. Light emitted from each LED is incident from the corresponding end of the light guiding body to the inside thereof and guided so as to be emitted from a light emitting surface of the light guiding body along the longitudinal direction thereof. Thus, the emitted light illuminates an original.
However, it is not easy to adjust the inclination angle distribution of the respective inclined surfaces that form the sawtooth-shaped light reflecting surface as shown in Patent Document 1. Regardless of how the inclination angle distribution of the respective inclined surfaces is adjusted, the emitted light quantity distribution not varies smoothly and a step occurs in the variation of the emitted light quantity distribution.
Also, when a plurality of light emitting devices is disposed on the end surface of the light guiding body as shown in Patent Document 2, the number of components and the costs are increased. Furthermore, in order to more appropriately set the emitted light quantity distribution emitted from the light emitting surface, it is necessary to further increase the number of the light emitting devices. Accordingly, the number of the components and the costs are more and more increased.
When the LED is disposed in the vicinity of the end of the light guiding body as shown in Patent Documents 3-5, the light guiding body may be heated and deformed by heat generation of the LED, because the light guiding body is made of synthetic resin such as acrylic resin. Also, recently, an original read speed in the image reading apparatus has been increased, and accordingly, a light quantity to illuminate the original has been increased. Thus, heat generation of the LED is increased and the lifetime thereof tends to be shortened. For this reason, a substrate with high heat dissipation efficiency is adopted to mount the LED, or a heat dissipation plate is overlapped with the substrate.
However, in Patent Document 3, the light guiding body, the LED substrate, the heat dissipation plate and the like are mounted on a frame. Part of the frame is located below the light guiding body and the LED substrate. Thus, air convection is decreased around the end of the light guiding body, the LED substrate, the heat dissipation plate and the like. This results in low heat dissipation efficiency of the LED substrate and the heat dissipation plate.
In Patent Documents 4 and 5, the heat dissipation plate extends outside the frame or the casing, thus heat dissipation efficiency of the heat dissipation plate is improved. However, since the LEDs and the light guiding body are disposed on the wall or in the inside of the frame or the casing, heat dissipation efficiency of the light guiding body and the LEDs is low.
The present invention was made in consideration of the above conventional problems. A first object of the present invention is to provide a light guiding body in which the emitted light quantity distribution can be smoothly varied and the number of components and the costs are not increased, an illuminating device that includes the light guiding body, and an image reading apparatus that includes the illuminating device. A second object of the present invention is to provide an image reading apparatus and an image forming apparatus in which high heat dissipation efficiency of the light guiding body can be maintained with a simple configuration.